1. Field of the Invention
Aspects of the present invention relate to a membrane-electrode assembly for a fuel cell, and a fuel cell system including the same. More particularly, aspects of the present invention relate to a membrane-electrode assembly that easily performs mass transfer and release, due to pores in a catalyst layer, and thereby improves fuel cell performance, and a fuel cell system including the same.
2. Description of the Related Art
A fuel cell is a power generation system for producing electrical energy, through an electrochemical redox reaction of an oxidant and hydrogen from a hydrocarbon-based material, such as, methanol, ethanol, or natural gas.
Such a fuel cell is a clean energy source that can reduce the need for fossil fuels. The fuel cell includes a stack of unit cells, and produces various ranges of power output. The fuel cell has four to ten times the energy density of a small lithium battery, and has accordingly been highlighted as a small portable power source.
Representative types of fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The direct oxidation fuel cell can be a direct methanol fuel cell that uses methanol as a fuel.
In a fuel cell, a fuel is supplied to an anode, adsorbed on catalysts of the anode, and oxidized to produce protons and electrons. The electrons are transferred to a cathode, via an external circuit, and the protons are also transferred to the cathode, through the polymer electrolyte membrane. In addition, an oxidant is supplied to the cathode, and then the oxidant, protons, and electrons are reacted on catalysts of the cathode, to produce electricity and water.
In the above fuel cell, the stack that generates electricity includes a plurality of unit cells, which are stacked in multiple layers, and each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly includes an anode (also referred to as a “fuel electrode” or an “oxidation electrode”), and a cathode (also referred to as an “air electrode” or a “reduction electrode”), which are separated by a polymer electrolyte membrane.